Binaural phase-discrimination radio system



March 24, 1931. n s. BRAND ETAL BINAURAL PHASvEDISC-RMINATION RADIO SYSTEM Filed Decztl- 20 1928- 2 Sheets-Sheet l 0,0 hump,...

Mrz; BY

ATTORNEY March 24, 1931 s. BRAND E'r AL BINAURAL PHASE DISCRIMINATION RADIO SYSTEM 2 Sheets-Sheet 2 Filed Dec. 20, 1928 Hamm..

INVENToRs 5. randon/y ATTORNEY 4,Patented Mar. 1931 UNITED s'ragras PATENT OFFICE sMAET EEAND, 0E EEooxLYN, AND PIERRE mEETz, 0E 4EELLEEosE MANoItNEw YoEE, AssIGNons To AMERICAN TELEPHONE AND TELEGEAPE conPANY, A conF PORATION F NEW YORK BINAUBAL PHASE-DISCRIMINATIUN RADIO'SYSTEM Application aleane'oember ao, was.` serial No. sanas-2.

This invention relates-to high frequency Asignaling systems and more particularly to a method of homodyner reception which may be utilized in such systems. The mvention furthermore relates to certain specific systems type of system itis essential that the carrier currents used for detection in the receiving set, whether transmitted ory generated local ly, should have definite, constant phase relationswith the carrier currents used at the transmitting station. It is one of the primary objects of the homodyne method of this invention to insure that tlfe vcarrier current used for detection in the'receiving set have definite and constant phase relations with the carrier currents used at the transmitting i station.

In accordance with the arrangements of the invention there will be provided at the receivingstation, a by-pass from the message channel. This willv lead to a modulator. in which the two transmitted signal' side bands are modulated together. Among the products ofmodulation will be the harmonics of the carrier frequency. A desirable one of these suoli as the second harmonic, is selected from the others by means of a tuned circuit or narrow band-pass filter, and used to'control the frequency and phase of a local oscillator of the carrier frequency.

Various methods of controlling the frequencyand phase of an oscillator by one of its harmonics are Well known. in the art. The method of control shown inthis invention, is simple coupling of the harmonic supply circuit With the grid circuit of the oscillator. The output of the oscillator will contain the carrier frequency and its harmonics.

The output from the oscillator is passed through an overloaded amplifier, whose power output will hence be substantially independent of its power inputfor normal inputs. The carrier frequency is selected by filter apparatus from the output ofthe amplifier and applied to a' demodulator in the usual way. By utilizing the reception method of this invention, it will be seen that the carrier current used for detection in the receiving set will'have definite and constant phase relationship with the carrier currents used at the transmitting station.

One of the particular uses to which thev homod ne reception method 'of the invention might e put is in a transmission system of the binaural type by means of which it is possible to give a listener an idea of the position of the source of sound producing the transmitted signal. i v

It is well known from the results of tests that the naturalness of 'sounds transmitted over electrical systems is greatly increased by the use of binaural transmission, i. e., transmitting -independently to each ear of the listener the sounds icked upby two transmitters separated rom each other by a distancenapproir'imately equal to that between the listeners ears. The use of phase discrim-f ination principles to obtain these two independent message channels for a radio system soy that the sounds vmay be transmitted binaurally over a singleradio frequency channel (this necessitating only one trans y mitting and one receivlng antenna system) has been ldisclosed in the art in a Patent #1,608,566, to R. K. Potter, November 30,

It is pointed out that in systems of the type illustrated in the above patent it is essential that the carrier currents used for detectionl in the receiving set, whether transmitted or generated locally, should have definite, constant phase relations withthe carrier currents used l at the transmitting station. @ne of the methods in the above mentioned types of systems has been to employ for this purpose the usual component'of the carrier frequency in the transmitted out ut.' This component will be the resultantofP-two. similar components l90" apart in phase,

independent message channels. has been found that there are important lim-- ita-tions in the use of said carrier component or resultant in this connection. This is due to the fact that, since the two channels are independent the components of the carrier frequency in these will vary in magnitude independently. This will vary the phase of the resultant with respect to either of the carrier components, thus violating the requirement that such phase angle be constant. Thisefect is more pronouncedV as the modulation is greater-the limitation therefore consists in the necessity of keeping the inodulationsmall.

In the particular embodiment of the al-,lk rangements of the invention as applied to a binaural transmission system, utilization is made of the well known fact that frequencies above 800 cycles do not give much binaural eifect. Consequently, these frequencies '(or say about 1,000 cycles, to give some margin) need be transmitted Aover only one channel, say, for example, the channel A. At the receiving end of the system a parallel' circuit in derivation to the main circuit is provided, passing only frequencies 1,000 cycles or more away from the carrier frequency. In other words, there will exist in this circuit two side bands resulting from the modulation from channel A alone. Accordingly this would eliminate any variations in phase of a resultant caused by independent modulation of its components from the two channels, respectively, as in former arrangements. These two bands' are then modulated together. Among the products kof, modulation v `will be the second harmonic ofthe carrier frequency. This will have a constant phase relation with the original carrier current, 1ndependent of the modulation. This 1s se- I lected from the others by a tuned circuit or narrow band pass filter and used to control the frequencyv and phase of an oscillator of Vthe carrier frequency. Various methods of controlling the frequency and phase of an oscillator bv one' of its harmonics are well known in the art. The method of controlshown inv this invention is simple coupling of the harmonic supply circuit with the gri circuit of the oscillator. The output of the oscillator will contain the carrier frequency and its harmonics. The fundamental is selected by means of a tuned circuit. or. narrow band pass filter. This current will have an unvarying phase relation with the modulated current in-channel A and. therefore, with that lin the other channel B. Itthen goes through a phase shifter to the phase discrimination apparatus. The last operation will be to sup ly the missin frequencies above 1,000 cyc es in channelB through a by-pass from channel A.

The invention may be more fully. under- 'known in the art.

one for each .of the twoh stood from` the following description, to- However, it l, gether with `the accompanyin may be applied to a binaural transmission system. n

In Fig. 1 is shown a circuit diagram ofa transmitter station for a high frequency signaling system. A transmitter 41 is shown connected to a balanced type of carrier suppression modulator 42 of which the two `vacunm tubes 4S and 44 are shown. An oscillator. 45 supplies the carrier frequency n. The antenna 4G is shown'. The balanced type of carrier suppression modulator 42 is well The current from the transmitter 41 modulates the output of oscillator. 45 and there will be impressed on the antenna 46 the two signal side ands, the carrier lbeing omitted. l

In Fig. 2 is shown a receiving system adapted to receive 'signals from the transmitting, station of Fig. 1 and comprising the arrangements of the invention. The receiving antenna 47 is shown connected to a message channel circuit 48. Bridged across circuit48 is a by-pass circuit 49 leading to a modulator 50. The two side bands transmitted from the arrangements of Fig. 1 are modulated together in the modulator 50. Among the products of modulation will be harmonics of the carrier frequency n. A desirable one of these such as the second harmonic 2n of the carrier frequency n will be selected fromthe others by means of a tuned circuit or narrow band-pass filter 51. It will then be applied to an oscillator 52 of the frequency n to control its phase and frequency. The second harmonic frequency supply circuit is simply coupled with the grid circuit of the oscillator. As is well known, this will keep the phase and frequency of the oscillator 52 the same as that of the carrier frequency 'n at the transmitting station. The output ofthe oscillator 52 is then passed through Van overloaded amplifier 53, whose power output will hence be substantially inependent of its power input, for normal inputs. yThe carrier frequency n is selected by the *lter 54 from the output of this amplifier and applied to the demodulator 55 in the usual way. The message currents will se arate channels A and. B may be transmitted tothe tubes M1 and M2 of a modulator of the well known duplex type.- Associated the modulator is an oscillator 6. Current from this oscillator, ofcarrier frequency, is passed through a resistance 7 and a condenser 8 in series. The potential differences across these will be 90 degrees out of phase with each other. On one .and another of these, respectively, are superimposed the modulating currents from channels A and B. After modulation the currents from the two channels will be transmitted to the antenna 9 for transmission to a distant station. 1t is pointed out that in circuit 4 there is inserted a low kpass filter 5 which Will'cut off frequencies which do not have any material binaural effect. such as frequencies about 1,000 cycles. Accordingly channel B Willv contain only frequencies below 1,000 cycles, while channel A will includeall frequencies in the signal range.

d cuit there might `be located a detector 11, a

local oscillator 12 and tuning devices. This would permit a receiving set of the arrange ments of the invention to be used in a broadcasting system where several broadcasting stations might be working on different wave lengths. A receiving set utilizing double detection as shown might'change reception from one broadcasting station to another without requiring a complicated change in the arrangements of filters in the set to be described hereinafter and sets might be made of uniform construction. n the above' arrangements the incomingmodulated radio frequency would firstl be beaten by the local oscillator 12 to produce a current of, say, 25.000 cycles, similarly modulated. The filtering arrangements of the sets could be designed to utilize such a frequency as a standard. The phase characteristics, which permit phase discrimination, are preserved throughout this modification. However, the above double detection scheme is not essential and is only illustrated as a. matter of choice. A The incoming modulated currents from the sending station of Fig. 3 might be received in a simple receiving circuit connected to thel antenna 10.

The receiving circuit connected to antenna 10 is divided into two parallel circuits 13 and 14. Circuit 13, which may include the amplifier 15, may be termed the message circuit and will transmit channels A and B to the detector and phase discrimination apparatus. This arrangement includes the detector tubes 25 and 26, the resistance 23 and condenser 24 arranged as shown, and is well known in the art. The circuit 14 is the circuit utilized for deriving the carrier frequency to be used for transmitting station. Inthe circuit 14 will be a band suppression filter 16. This filterwill be designed to suppress a ban'cl of frequencies 1,000 cycles on each side of the car istence of two side bands from the channel A only, or the portion thereof above 1,000 cycles. This will eliminate the defect in former systems of a variation in phase of the resultant carrier due to modulation of the carrier by both channels. These two side bands 1,000 cycles away from the carrier will be modulated together in the modulator 17. Among the products of modulation will be the second harmonic of the carrier frequency. This second harmonic will be selected from the others by the filter 18 and used to control the frequency and phase of an oscillator 19 of "the carrier frequency. Various methods of controlling the frequency and phase of an oscillator by one of its harmonics are well known in the art. The method. of control illustrated is simple coupling of the harmonic supply circuit with the grid circuit of the oscillator. The output of the oscillator will contain the carrier frequency and its harmonies. The fundamental is selected by means of the filter 20. This current will have an unvarying phaserelation with the modulated current in channel A and, therefore,

also with that in channel B. It then goes through the phase shifter 21 and the amplifier 22 to the phase discrimination apparatus heretofore referred to which is well known in the art. The outputs of the two detector tubes 25 and26 are connected respectively by the circuits -27 and 28 to the receivers 30 and 31 forbinaura-l reception. The missing frequencies above 1,000 cycles in channel B are supplied thereto. through a by-pass circuit, from channel A including the filter 29 which passes frequencies above 1,000 cycles. It will be noted that the required phase relations hold only when the circuit is in actual use, as it requires a modulating current in channel A ofa frequency over 1,000 cycles. When the circuit is idle there will be no control over the phase of the oscillator 19, but, of course, none will be needed. As soon as the circuit is in use again, signals will be sent over channel A and current will flow to control the phase of the oscillator 19. There will be `a short interval of time required before this control is accurate, but this will be only a few cycles of the carrier frequency and will be imperceptible to the ear. Since the oscillator 19 is controlled by its second harmonic there may occur ka phase change of 180 after the'silent period. This corresponds to a reversal in poling of both the re- A ceivers and willV therefore have no effect on the ear.

This application is a continuation in fpart of our application, Serial No. 230,888, led November 3, 1927.

While the invention has been described in certain specific arrangements which are deemed desirable, it is understood that it is capable of embodiment in many and other Widely varied forms without departin from `the spirit of the invention as defined y the ,ap ended claims.

hat is claimed is: q

V1. In a system for the binaural transmission of si nals the method which consists in the modu ation of a carrier by signal variations resulting from sound waves, producing another set of signal variations resulting from sound waves from the same source but with fre uencies in a band not materially contributing to the binaural effect eliminated therefrom, modulating by said second set of signal variations carrier oscillations of the same frequency as employed in the first mentioned modulation o eration but differing in phase by 90 there rom, and transmitting both sets of side bands.

2. In a system for the binaural transmission of signals the method which consists in the modulation of a carrier by signal variations resulting from sound waves, producing another set of signal variations resulting from sound waves from the same source but with fre uencies in a band not materially contributing to the binaural effect eliminated therefrom, modulating by said second setof signal variations carrier oscillations of the same frequency as employed in the first mentioned modulation o eration but differing in phase by 90 there rom, transmitting both sets of side bands, lderiving at the receiving station from the transmitted side bands, two side bands including only those frequency com onents notmaterially contributin to the inaural effect, combining the derived side bands to produce a resultant frequency related to the corresponding carrier, and

controlling the phase and frequency of the carrier used for detection by said resultant requency.

3'. In a system for the binaural transmission of si als the method which consists in the modu ation of a carrier by signal variation's resulting from sound waves, producing another set of signal variations resulting from sound Waves from the same source but with frequencies above 1,000 cycles eliminated therefrom, modulating by said second set of signal variations carrier oscillations of the same frequency as employed in the first mentioned modulation operation but differing in `phase b 90 therefrom, transmitting both sets of si e bands, producing at the receivin station from said resultant carrier de bands having frequency limits 1,000

two si cycles away from said carrier, combinin the derived side bands to produce a res tant frequency related to the corresponding carrier and controlling the (phase and frequency ofthe carrier used for etection by said resultant frequency.

4. In a high frequency signaling system the method of receiving messages which comprises modulating the'transmitted side ban s together without the correspondin carrier, selecting from the product of suc modulation one of the harmonics of the carrier frequencyto which the side bands correspond, and utilizing said selected harmonic frequency to control the phase and frequency of the local carrier frequency utilized for detection.

5.Inahihfre the method o receiving messages which comprises modulating the transmitted side bands `together without the corresponding carrier,

ecting from the product of such modulation a desirable harmonic of the carrier frequency to which the side bands correspond, utilizing said selected harmonic frequency to control the phase and frequency of a locall generated carrier frequency so that it wil have a predetermined frequencyand phase relationship with respect to the carrier used at the transmitting station, and utilizing 'said locally generated carrier fre uency as so controlled for detecting sai transmitted side bands.

6. A high frequency signaling system comprisin a transmitting station, means whereby t e carrier is suppressed from the side bands, a receivin demodulator, a circuit whereby said side ands may be ap lied to the input of said demodulator, a ocal oscillator connected to said demodulator, a circuit in arallel with said demodulator input circuit, a modulator in said circuit to which said side bands are applied, selective means associated with said modulator output for selecting aharmonic of the carrier frequency corresponding to the plied side bands, and means to cou le pqtput of said selective means to said oscila or.

7. high frequency signaling system comprisin a transmitting station, means whereby t e carrier is su pressed from the side bands, a receiving emodulator, a receivin circuit for said side bands connected to sai demodulator, avsecond-circuit oonnected to said receiv' circuit a modulator in said circuit to whic said side bands are apphed, select-ive means in said circuit connected to said modulator output for selecting a harmonic of the carrier, uency corresponding to the-applied side bands, an oscil lator having its mput circuit'coupled to said selective means, a second selective means connected to the output of said oscillator for selecting a currentfof thefreqiiencyof said quency signaling system I lll carrier, and means to impress said selected current on said demodulator for vdetecting said side bands. I

- In testimony whereof2 we have signed our names to this specification this 17t day' of- December, 1928.

SMART BRAND. `PIERRE MERTZ. 

